1. Field of the Invention
This invention relates to ductile iron pipe joints, and more particularly to such a pipe joint employing a coupling element forming a fluid tight high strength coupling suitable for use in trenchless pipe installations.
2. Description of the Prior Art
It is frequently necessary or desirable to install underground pipe without digging an open trench for placing the pipe. For example, in installing new water or sewer systems or replacing old pipe in an urban area, it is often necessary to place a pipe beneath an existing road, street or railroad where it is not practical to interrupt traffic for a time sufficient to cut an open trench across the roadway, install the pipe, backfill the trench, and replace the roadway. In such cases, it is known to install the pipe in such a trenchless operation by pushing the pipe through the soil beneath the roadway, and one system for installing pipe in a trenchless operation is disclosed, for example, in U.S. Pat. No. 5,205,671 to Handford.
Although conventional bell and spigot joints of the type employed in ductile iron pipe are capable of withstanding substantial axial compressive loads, such joints are not designed to carry loads of the magnitude frequently required to push pipe into place in a trenchless operation. Further, the increased diameter of the bell results in a substantial increase in the load required to push the pipe through the soil and results in a substantial, concentrated radial compressive load on the pipe at the joint. It is, therefore, an object of the present invention to provide a high strength, leak-proof coupling for ductile iron pipe for use in a trenchless pipe installation.
Another object is to provide such a pipe joint having a substantially smooth outside diameter substantially equal to the outside diameter of the pipe joined.
Another object is to provide such a pipe joint employing a high strength coupling element which does not materially interfere with the flow of fluids through the pipe.
Another object is to provide such a high strength pipe joint employing a coupling element capable of transmitting substantial axial compressive loads between two lengths of pipe joined by the coupling.
Another object is to provide such a pipe joint coupling including a coupling which may be interlocked with the pipe to provide a restrained joint.